1. Field of the Invention
The present invention concerns a method for reorienting cardiac images that are among a number of successively obtained cardiac images, and in particular to such a method that is implemented in a computerized processor.
2. Description of the Prior Art
Images of the heart for medical diagnosis may be produced using a PET (Positron Emission Tomography) imaging modality or SPECT (Single Particle Emission Computed Tomography) imaging modality. PET or SPECT imaging does not directly detect the location of body features. Rather, a tracer is introduced into a patient's bloodstream, and the location and density of the tracer is detected. An effect of this is that early images show the location of blood, carrying the tracer. Later images show the position of muscle tissue such as myocardium, once tracer has been absorbed into the muscle tissue. The heart may accordingly be imaged in two distinct phases—early frames, which represent the location of volumes of blood within the heart, and late frames, which represent the location of myocardium: muscle tissue of the heart.
It is often required in cardiac imaging to perform segmentation and reorientation of the Left Ventricle (LV) of the heart. The reorientation is performed such that the LV can be displayed with its main—longest—axis being shown horizontally or vertically. Such views are conventionally known as the long- and short-axis views.
Such reorientation must deal with several challenges, for example:
Defects in the myocardium uptake represented on late frames may cause ambiguous reorientation judgments, whether the reorientation judgments are performed by a human operator or an automatic algorithm.
A corresponding early frame image, which shows the shape and position of a blood pool, can be used to aid the reorientation to ensure that the correct reorientation angle is used.
FIG. 1A shows an example late frame, indicating myocardium position, and FIG. 1B shows a corresponding early frame, indicating blood position, at a first reorientation angle.
FIG. 1C shows an example late frame, indicating myocardium position, and FIG. 1D shows a corresponding early frame, indicating blood position, at a second reorientation angle.
FIGS. 2A-2D show corresponding images for a different patient. This patient has a left ventricle with a curved shape. In such cases, the early frame blood pool image may be used to help to achieve a consistent result.
FIG. 2A shows an example late frame, indicating myocardium position, and FIG. 2B shows a corresponding early frame, indicating blood position, at a first reorientation angle.
FIG. 2C shows an example late frame, indicating myocardium position, and FIG. 2D shows a corresponding early frame, indicating blood position, at a second reorientation angle.
Conventional practice is to perform a visual inspection and reorientation based on the late frame or a summed late frame image of the myocardium only. This can lead to errors in further processing of the image data, especially when it comes to comparing multiple datasets. The early frame blood pool image is not usually checked.
Known automatic reorientation methods have been found to generate unsatisfactory results. These results may be improved by use of a corresponding early frame blood pool information to assist in reorientation of a late frame myocardium image.
FIG. 3A shows an example late frame, indicating myocardium position, and FIG. 3B shows a corresponding early frame, indicating blood position, at an initial, inappropriate, reorientation angle.
FIG. 3C shows an example late frame, indicating myocardium position, and FIG. 3D shows a corresponding early frame, indicating blood position, at an improved reorientation angle.